The train ride home took two hours and seventeen minutes—exactly the time Alex needed to let the equations settle.
He had left campus at dawn on Saturday, backpack light, sketchbook locked in the bottom drawer of his desk. The nor'easter had moved on, leaving the New England hills washed clean and the sky the color of ungraded paper. By the time the train pulled into the small station in Maple Ridge, his mother was already waiting on the platform in her faded green coat, waving with both hands like he was still twelve.
"Alexander," she said, pulling him into a hug that smelled of rosemary and laundry detergent. "You look thinner. They don't feed you at that fancy school?"
"Campus food is adequate," he answered, the same word Sophia would have used. He let the hug last four seconds—long enough to be polite, short enough to remain himself.
His father waited in the car, engine running. Richard Rivera was a civil engineer who measured everything in tolerances and load-bearing capacity. He gave Alex a firm handshake and a single nod.
"Midterms treating you fair?" he asked as they pulled out of the lot.
"Fair enough. One professor's impossible. The rest are manageable."
His mother laughed from the passenger seat. "That's my boy. Always measuring. You get that from your father."
Dinner was at six-thirty sharp—roast chicken, garlic mashed potatoes, green beans from the garden his mother still tended even though the kids were gone. They ate at the same oak table where Alex had done every math worksheet from age six onward. His father asked about his literature thesis; his mother asked if he was seeing anyone. Alex gave the same answer to both questions.
"Nothing serious. Focus first."
His mother's fork paused mid-air. "Focus is good, sweetheart. But you're twenty-one tomorrow. A little life outside the books won't kill you."
Alex smiled the small, closed smile he used when the data didn't support the hypothesis. "Life's already interesting enough."
They talked about his sister in Seattle, about the new bridge his father was designing, about the neighbor's dog that kept digging under the fence. Normal vectors. Safe constants. No one asked why he sometimes stared at his phone like it might bite him. No one mentioned the three women whose orbits had begun to intersect in ways that defied every clean equation he had ever trusted.
After dinner he helped clear the table, loaded the dishwasher in the exact pattern his mother preferred, then went upstairs to his childhood room. The same posters—Feynman diagrams, a faded print of Escher's impossible stairs—still hung above the desk. He set his alarm for seven, lay down fully clothed, and slept without dreaming.
Sunday morning arrived on schedule.
He woke at 6:58, made his bed with hospital corners, and walked the six blocks to the public library where he had tutored local high-school kids for the last four summers. Three students waited: a nervous sophomore struggling with calculus, a senior rewriting her college essay, and a quiet freshman who simply needed someone to sit with her while she read. Alex gave each of them exactly what they required—clear steps, quiet encouragement, zero wasted words. By noon he had earned two hundred dollars and the same sense of equilibrium he always found in teaching: input, process, output. Clean.
He studied for three hours in the library's back corner—re-reading Eliot, annotating in the margins with the same red pen Sophia used. Then he packed up, hugged his mother goodbye at the front door (four seconds again), shook his father's hand, and caught the 4:17 train back to Eldridge.
The campus looked different under Sunday-evening light—quieter, almost expectant. His dorm hallway smelled of popcorn and laundry. He dropped his bag, showered, and changed into the one decent button-down he owned.
Because today—technically midnight onward—was his birthday.
He had told no one. Not Sophia. Not Mia. Not Bella. Birthdays were variables, not constants. He had planned to spend it alone with a book and a quiet beer.
But when he stepped into the small common room on the third floor at eight-thirty, the lights were already low and someone had taped a single crooked "Happy Birthday" banner above the microwave. Three people waited.
Mia stood by the window, hood up, sketchbook under her arm. She didn't smile. She simply lifted the book half an inch in silent offering.
Bella leaned against the counter in a navy sweater that cost more than his entire wardrobe, arms folded, one eyebrow arched exactly as it had been the night of the blackout.
And Sophia—Professor Sophia Lang, who should not have been anywhere near undergraduate housing—sat on the edge of the couch in a dark coat, legs crossed, holding a small rectangular box wrapped in plain brown paper.
None of them spoke first.
Alex stopped in the doorway and felt the geometry shift again, the angles tightening by another invisible degree.
Sophia's voice cut the silence, cool and precise.
"Mr. Rivera. We heard a rumor. Twenty-one is a significant prime number. It seemed… inefficient to let it pass without acknowledgment."
Mia opened her sketchbook to a fresh page. The first line she drew was the exact curve of his left shoulder.
Bella pushed off the counter and set a bottle of decent scotch beside a single plastic cup.
"Drink or don't," she said. "But if you're going to measure the evening, at least use proper units."
Alex closed the door behind him.
The room was small. The distances between the four of them were still perfect, still consistent.
But for the first time, the four-body problem had invited itself to his birthday.
And none of them looked like they planned to leave early.